Boroalumino silicate glasses

ABSTRACT

Disclosed are alkali-free glasses having a liquidus viscosity of greater than or equal to about 90,000 poises, said glass comprising SiO 2 , Al 2 O 3 , B 2 O 3 , MgO, CaO, and SrO such that, in mole percent on an oxide basis: 64≦SiO 2 ≦68.2; 11≦Al 2 O 3 ≦13.5; 5≦B 2 O 3 ≦9; 2≦MgO≦9; 3≦CaO≦9; and 1≦SrO≦5. The glasses can be used to make a display glass substrates, such as thin film transistor (TFT) display glass substrates for use in active matrix liquid crystal display devices (AMLCDs) and other flat panel display devices.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to U.S. provisionalapplication No. 61/130,474, filed on May 30, 2008 and entitled“BOROALUMINO SILICATE GLASSES,” the content of which is relied upon andincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates, generally, to glasses and, moreparticularly, to boroalumino silicate glasses and to methods for makingand using same.

BACKGROUND

Displays may be broadly classified into one of two types: emissive(e.g., CRTs and plasma display panels (PDPs)) or non-emissive. Thislatter family, to which liquid crystal displays (LCDs) belong, reliesupon an external light source, with the display only serving as a lightmodulator. In the case of liquid crystal displays, this external lightsource may be either ambient light (used in reflective displays) or adedicated light source (such as found in direct view displays).

Liquid crystal displays rely upon three inherent features of liquidcrystal (LC) materials to modulate light. The first is the ability of LCmaterials to cause optical rotation of polarized light. Second is thedependence of such rotation on the mechanical orientation of the liquidcrystal. Third is the ability of the liquid crystal to undergomechanical orientation by the application of an external electric field.

In the construction of a simple, twisted nematic (TN) liquid crystaldisplay, two substrates surround a layer of liquid crystal material. Ina display type known as Normally White, the application of alignmentlayers on the inner surfaces of the substrates creates a 90° spiral ofthe liquid crystal director. This means that the polarization oflinearly polarized light entering one face of the liquid crystal cellwill be rotated 90° by the liquid crystal material. Polarization films,oriented 90° to each other, are placed on the outer surfaces of thesubstrates.

Light, upon entering the first polarization film becomes linearlypolarized. Traversing the liquid crystal cell, the polarization of thislight is rotated 90° and is allowed to exit through the secondpolarization film. Application of an electric field across the liquidcrystal layer aligns the liquid crystal directors with the field,interrupting its ability to rotate light. Linearly polarized lightpassing through this cell does not have its polarization rotated andhence is blocked by the second polarization film. Thus, in the simplestsense, the liquid crystal material becomes a light valve, whose abilityto allow or block light transmission is controlled by the application ofan electric field.

The above description pertains to the operation of a single pixel in aliquid crystal display. High information type displays require theassembly of several million of these pixels, which are referred to inthe art as sub pixels, into a matrix format. Addressing all of these subpixels, i.e., applying an electric field to all of these sub pixels,while maximizing addressing speed and minimizing cross-talk presentsseveral challenges. One of the preferred ways to address sub pixels isby controlling the electric field with a thin film transistor located ateach sub pixel, which forms the basis of active matrix liquid crystaldisplay devices (AMLCDs).

The manufacturing of these displays is extremely complex, and theproperties of the substrate glass can be extremely important whenproducing displays having optimal performance. We have described somesuitable substrate glasses in U.S. Pat. No. 6,060,168 to Kohli, U.S.Pat. No. 6,319,867 to Chacon et al., U.S. Pat. No. 6,831,029 to Chaconet al., and U.S. Pat. No. RE38,959 to Kohli. However, a need for glassesthat can be used as substrates in the manufacture of active matrixliquid crystal display devices (AMLCDs) and other flat panel displayscontinues to exist, and the present invention is directed, in part, toaddressing this need.

One technical issue facing the glass substrates for LCD displays,especially those displays made by high-temperature processes such aspolysilicon technology, is the density change (compaction, or thermalstability) of the glass sheets after they are subjected tohigh-temperature treatment steps. The compaction of the glass sheets canlead to lack of registration of the semiconductor features created onthe surface of the substrates, hence lower-quality or defectivedisplays. Thermal stability of the glass sheet is dependent on the glasscomposition and thermal history thereof. Whereas a rigorously annealedglass sheet would have less compaction in down-stream processing,obtaining such thermodynamically stable glass sheet is difficult andcould incur prohibitive costs to the manufacture process by requiringeither a secondary heat treatment and/or a low production rate. It hasbeen found that anneal point of the glass material correlates with thethermal stability of a glass sheet. For glass sheets produced by a giventhermal process, the higher the anneal point of the glass material, theless the compaction of the glass sheets made therefrom.

The present invention addresses the various technical issues discussedsupra.

SUMMARY

The present invention relates to an alkali-free glass having a liquidusviscosity of greater than or equal to about 90,000 poises, said glasscomprising SiO₂, Al₂O₃, B₂O₃, MgO, CaO, and SrO such that, in molepercent on an oxide basis:64≦SiO₂≦68.2;11≦Al₂O₃≦13.5;5≦B₂O₃≦9;2≦MgO≦9;3≦CaO≦9; and1≦SrO≦5.

These and additional features and embodiments of the present inventionwill be more fully illustrated and discussed in the following drawingsand detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing compaction after one hour at 450° C. forglasses with a range of anneal points.

FIG. 2 is a graph of predicted SiO₂ content vs. measured SiO₂ contentfor a variety of glasses in accordance with the present invention.

FIG. 3 is a graph of predicted MgO content vs. measured MgO content fora variety of glasses in accordance with the present invention.

FIG. 4 is a graph of melting temperature of various glasses of thepresent invention as a function of SiO₂ content.

DETAILED DESCRIPTION

Before the present materials, articles, and/or methods are disclosed anddescribed, it is to be understood that the aspects described below arenot limited to specific materials, preparative methods, or uses, but isto be understood to be illustrative of the invention. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular aspects only and is not intended to be limiting.

Throughout this specification and claims, unless the context requiresotherwise, the word “comprise” or variations, such as “comprises” or“comprising”, will be understood to imply the inclusion of a statedelement but not the exclusion of any other element or group of elements.

It must be noted that, as used in the specification and the appendedclaims, the singular forms “a”, “an”, and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a fining agent” is meant to include mixtures of two ormore such fining agents; reference to “the glass former” is meant toinclude mixtures of two or more such glass formers; and the like.

“Optional” or “optionally” means that the subsequently described eventor circumstance can or cannot occur, and that the description includesinstances where the event or circumstance occurs and instances where itdoes not.

When values are expressed as approximations, e.g., by use of theantecedent “about” as in “‘about’ a particular value”, it will beunderstood that the particular value forms another aspect of theinvention. Ranges may be expressed herein as “from ‘about’ oneparticular value to ‘about’ another particular value”, as “less than‘about’ a particular value”, as “‘about’ a particular value or greater”,etc. When such ranges are expressed, another aspect of the inventionincludes “from the one particular value to the other particular value”,“less than the particular value”, and “the particular value or greater”,respectively. It will be further understood that the endpoints of eachof the ranges are significant both in relation to the other endpoint,and independently of the other endpoint; and, in cases where no lowerendpoint is stated in a range, the lower endpoint is meant to be andinclude zero.

A weight percent of a component, unless specifically stated to thecontrary, is based on the total weight of the formulation or compositionin which the component is included. Similarly, a mole percent of acomponent, unless specifically stated to the contrary, is based on thetotal number of moles of all components in the formulation orcomposition in which the component is included.

As discussed above, the present invention relates to an alkali-freeglass that includes SiO₂, Al₂O₃, B₂O₃, MgO, CaO, and SrO, and the glasscan further include a variety of other components. The SiO₂, Al₂O₃,B₂O₃, MgO, CaO, SrO, and other components (if any) are chosen such thatthe glass includes, as calculated in mole percent on an oxide basis:64-68.2SiO₂, 11-13.5Al₂O₃, 5-9B₂O₃, 2-9, MgO, 3-9CaO, and 1-5SrO.

As used herein, “alkali-free” means that the glass (i) is essentiallyfree of intentionally added alkali metal oxide, for example, to avoidthe possibility of having a negative impact on thin film transistor(TFT) performance through diffusion of alkali ions from the glass intothe silicon of the TFT; (ii) contains a total of less than about 0.1 mol% of alkali metal oxides; or (iii) both.

In certain embodiments, the glass includes, as calculated in molepercent on an oxide basis, 64-68SiO₂. In certain embodiments, the glassincludes, as calculated in mole percent on an oxide basis,11.3-13.5Al₂O₃.

In certain embodiments, the glass satisfies one or more of the followingexpressions:1.05≦(MgO+CaO+SrO)/Al₂O₃≦1.45;0.67≦(SrO+CaO)/Al₂O₃≦0.92; and0.45≦CaO/(CaO+SrO)≦0.95.

For example, in certain embodiments, the glass satisfying the aboveimmediate requirements further has a liquidus temperature of lower thanor equal to about 1200° C., and a melting temperature of lower than orequal to about 1620° C.

For example, in certain embodiments, the glass satisfies the first ofthe aforementioned expressions (1.05≦(MgO+CaO+SrO)/Al₂O₃≦1.45). Incertain embodiments, the glass satisfies the second of theaforementioned expressions (0.67≦(SrO+CaO)/Al₂O₃≦0.92). In certainembodiments, the glass satisfies the third of the aforementionedexpressions (0.45≦CaO/(CaO+SrO)≦0.95). In certain embodiments, two ormore of the aforementioned expressions are satisfied. In certainembodiments, all three of the aforementioned expressions are satisfied.By way of further illustration, in certain embodiments, the glasssatisfies all three of the following expressions:1.05≦(MgO+CaO+SrO)/Al₂O₃≦1.3;0.72≦(SrO+CaO)/Al₂O₃≦0.9; and0.55≦CaO/(CaO+SrO)≦0.95,such as in the case where the glass satisfies all three of the followingexpressions:1.05≦(MgO+CaO+SrO)/Al₂O₃≦1.3;0.72≦(SrO+CaO)/Al₂O₃≦0.9; and0.8≦CaO/(CaO+SrO)≦0.95.

The glasses of the present invention (e.g., any of the glasses discussedabove) can further include a variety of other components.

For example, the glasses of the present invention can further includeSnO₂, Fe₂O₃, CeO₂, As₂O₃, Sb₂O₃, Cl, Br, or combinations thereof. Thesematerials can be added as fining agents (e.g., to facilitate removal ofgaseous inclusions from melted batch materials used to produce theglass) and/or for other purposes. In certain embodiments, the glasses ofthe present invention (e.g., any of the glasses discussed above) furtherinclude SnO₂ (e.g., as calculated in mole percent on an oxide basis,0.02-0.3SnO₂, etc.) and Fe₂O₃ (e.g., as calculated in mole percent on anoxide basis, 0.005-0.08Fe₂O₃, 0.01-0.08Fe₂O₃, etc.). By way ofillustration, in certain embodiments, the alkali-free glass of thepresent invention further includes SnO₂ and Fe₂O₃, wherein, in molepercent on an oxide basis:0.02≦SnO₂≦0.3; and0.005≦Fe₂O₃≦0.08.

In certain embodiments, the glasses of the present invention includeless than 0.05% (e.g., less than 0.04%, less than 0.03%, less than0.02%, less than 0.01%, etc.) by weight of Sb₂O₃, As₂O₃, or combinationsthereof. In certain embodiments, the glasses of the present inventionfurther include SnO₂, Fe₂O₃, CeO₂, Cl, Br, or combinations thereof andinclude less than 0.05% (e.g., less than 0.04%, less than 0.03%, lessthan 0.02%, less than 0.01%, etc.) by weight of Sb₂O₃, As₂O₃, orcombinations thereof. In certain embodiments, the glasses of the presentinvention further include SnO₂ and Fe₂O₃ and include less than 0.05%(e.g., less than 0.04%, less than 0.03%, less than 0.02%, less than0.01%, etc.) by weight of Sb₂O₃, As₂O₃, or combinations thereof. Incertain embodiments, the alkali-free glasses of the present inventionfurther include SnO₂ and Fe₂O₃, wherein, in mole percent on an oxidebasis:0.02≦SnO₂≦0.3; and0.005≦Fe₂O₃≦0.08,and include less than 0.05% (e.g., less than 0.04%, less than 0.03%,less than 0.02%, less than 0.01%, etc.) by weight of Sb₂O₃, As₂O₃, orcombinations thereof.

The glasses of the present invention (e.g., any of the glasses discussedabove) can include F, Cl, or Br, for example, as in the case where theglasses further include Cl and/or Br as fining agents. For example, theglass can include fluorine, chlorine, and/or bromine, wherein, ascalculated in mole percent: F+Cl+Br≦0.4, such as where F+Cl+Br≦0.3,F+Cl+Br≦0.2, F+Cl+Br≦0.1, 0.001≦F+Cl+Br≦0.4, and/or 0.005≦F+Cl+Br≦0.4.By way of illustration, in certain embodiments, the glass furtherincludes SnO₂ and Fe₂O₃ and, optionally, fluorine, chlorine, and/orbromine, such that, as calculated in mole percent on an oxide basis:0.02≦SnO₂≦0.3, 0.005≦Fe₂O₃≦0.08, and F+Cl+Br≦0.4; and, in certainembodiments, the glass further includes SnO₂ and Fe₂O₃ and, optionally,Sb₂O₃, As₂O₃, fluorine, chlorine, and/or bromine, such that, ascalculated in mole percent on an oxide basis, 0.02≦SnO₂≦0.3,0.005≦Fe₂O₃≦0.08, and F+Cl+Br≦0.4, and such that the glass includes lessthan 0.05% (e.g., less than 0.04%, less than 0.03%, less than 0.02%,less than 0.01%, etc.) by weight of Sb₂O₃, As₂O₃, or combinationsthereof.

The use of SnO₂, Fe₂O₃, CeO₂, As₂O₃, Sb₂O₃, Cl, Br, or combinationsthereof as fining can be especially useful in the manufacture of glassesfor certain applications, such as substrates for flat panel displays. Asmentioned above, fining agents can be added, for example, to produceglasses that are substantially defect-free by facilitating removal ofgaseous inclusions from melted batch materials used to produce theglass. Illustratively, iron/tin fining can be used alone or incombination with other fining techniques if desired. For example,iron/tin fining can be combined with halide fining, e.g., brominefining. However, halide fining presents challenges from a pollutionabatement point of view, and halides can complex with iron to produceglass with non-optimal transmission characteristics. Other possiblecombinations include, but are not limited to, iron/tin fining plussulfate, sulfide, cerium oxide, mechanical bubbling, and/or vacuumfining. However, optimization may require that the sulfur content of theglass be controlled to avoid the production of gaseous defectscontaining SO₂ or SO₃; and the use of excessive amounts of iron or othertransition metal fining agents may impart undesirable coloration to theglass.

The glasses of the present invention can further include BaO. In certainembodiments, the glasses of the present invention include less than 1000ppm by weight of BaO.

As noted above, the glasses of the present invention are “alkali-free”.As also noted above, the alkali-free glasses of the present inventioncan include alkali oxides (e.g., Li₂O, Na₂O, K₂O, etc), provided thatthe glass (i) is essentially free of intentionally added alkali metaloxide; (ii) contains a total of less than about 0.1 mol % of alkalimetal oxides; or (iii) both. For example, in those cases where the glassis to be used as a thin film transistor (TFT) substrate, the intentionalinclusion of alkali oxides is generally viewed as being undesirableowing to their negative impact on TFT performance. In certainembodiments, the alkali-free glass of the present invention includesintentionally added alkali oxides, but in amounts such that thealkali-free glass contains less than 1000 ppm (e.g., less than 700 ppm,less than 500 ppm, less than 200 ppm, less than 100 ppm, less than 50ppm, etc.) by weight of alkali oxides (e.g., in amounts such that thesum of Li₂O, Na₂O, and K₂O is less than 1000 ppm by weight). In certainembodiments, the alkali-free glass of the present invention includes nointentionally added alkali oxides, and the alkali-free glass contains atotal of less than about 0.1 mol % of alkali metal oxides.

The glasses of the present invention can further include contaminants astypically found in commercially prepared glass. In addition oralternatively, a variety of other oxides (e.g., TiO₂, MnO, ZnO, Nb₂O₅,MoO₃, Ta₂O₅, WO₃, ZrO₂, Y₂O₃, La₂O₃, and the like) can be added so longas their addition does not push the composition outside of the rangesdescribed above. In those cases where the glasses of the presentinvention further include such other oxide(s), each of such other oxidesare typically present in an amount not exceeding 1 mole percent, andtheir total combined concentration is typically less than or equal to 5mole percent, although higher amounts can be used so long as the amountsused do not place the composition outside of the ranges described above.The glasses of the invention can also include various contaminantsassociated with batch materials and/or introduced into the glass by themelting, fining, and/or forming equipment used to produce the glass(e.g., ZrO₂).

As mentioned above, in certain embodiments, the glass satisfies one ormore of the following expressions:1.05≦(MgO+CaO+SrO)/Al₂O₃≦1.45;1.05≦(MgO+CaO+SrO)/Al₂O₃≦1.3;0.67≦(SrO+CaO)/Al₂O₃≦0.92;0.72≦(SrO+CaO)/Al₂O₃≦0.9;0.45≦CaO/(CaO+SrO)≦0.95;0.55≦CaO/(CaO+SrO)≦0.95; and0.8≦CaO/(CaO+SrO)≦0.95.

Irrespective of whether the glass satisfies none, one, two, or three, ormore of the aforementioned expressions and irrespective of whether theglass contains none, one, or more of additional components (e.g., thosediscussed above), the SiO₂, Al₂O₃, B₂O₃, MgO, CaO, SrO, and othercomponents (if any) can be chosen such that, in mole percent on an oxidebasis:−0.3≦SiO₂−[SiO₂]_(pred)≦0.3 and−0.3≦MgO−[MgO]_(pred)≦0.3in which[SiO₂]_(pred)=[87.57−6.06×MgO/B_(o)+66.54×R_(o)−80.61×S_(o)]×B_(o)[MgO]_(pred)=[1.29+12.94×R_(o)−14.4×S_(o)]×B_(o)and in whichR_(o)=(MgO+CaO+SrO)/Al₂O₃S_(o)=(CaO+SrO)/Al₂O₃B_(o)=1−B₂O₃/100.

Additionally or alternatively, the SiO₂, Al₂O₃, B₂O₃, MgO, CaO, SrO, andother components (if any) can be chosen such that:0.45≦CaO/(CaO+SrO)≦0.8; such that 64≦SiO₂≦68; such that 11.3≦Al₂O₃≦13.5;such that 0.02≦SnO₂≦0.3; such that 0.005≦Fe₂O₃≦0.08; such thatF+Cl+Br≦0.4; and/or such the glass includes less than 0.05% (e.g., lessthan 0.04%, less than 0.03%, less than 0.02%, less than 0.01%, etc.) byweight of Sb₂O₃, As₂O₃, or combinations thereof.

As mentioned above, the glasses of the present invention include5-9B₂O₃. Examples of such glasses include those in which contain, ascalculated in mole percent on an oxide basis: 5-8.8B₂O₃, 5-8.5B₂O₃,5-8.2B₂O₃, and/or 5-8B₂O₃.

Also as mentioned above, the glasses of the present invention include2-9MgO. Examples of such glasses include those which contain, ascalculated in mole percent on an oxide basis: 2-8MgO, 2-7MgO, 2-6MgO,2.5-9MgO, 2.5-8MgO, 2.5-8MgO, 2.5-7MgO and/or 2.5-6MgO.

Also as mentioned above, the glasses of the present invention include1-5SrO. Examples of such glasses include those which contain, ascalculated in mole percent on an oxide basis: 1-4.5SrO, 1-4SrO,1-3.5SrO, 1.5-5SrO, 1.5-4.5SrO, 1.5-4SrO, 1.5-3.5SrO, 2.5-3.5SrO, and/or2.5-5SrO.

In certain embodiments, the SiO₂, Al₂O₃, B₂O₃, MgO, CaO, SrO, and othercomponents (if any) are chosen such that the glass includes, ascalculated in mole percent on an oxide basis: 64-68.2SiO₂, 11-13.5Al₂O₃,5-9B₂O₃, 2-9, MgO, 3-9CaO, and 1-3.5SrO.

In certain embodiments, the SiO₂, Al₂O₃, B₂O₃, MgO, CaO, SrO, and othercomponents (if any) are chosen such that the glass includes, ascalculated in mole percent on an oxide basis: 64-68.2SiO₂, 11-13.5Al₂O₃,5-9B₂O₃, 2.5-6, MgO, 3-9CaO, and 1-5SrO.

In certain embodiments, the SiO₂, Al₂O₃, B₂O₃, MgO, CaO, SrO, and othercomponents (if any) are chosen such that the glass includes, ascalculated in mole percent on an oxide basis: 64-68.2SiO₂, 11-13.5Al₂O₃,5-8B₂O₃, 2-9, MgO, 3-9CaO, and 1-5SrO.

In certain embodiments, the SiO₂, Al₂O₃, B₂O₃, MgO, CaO, SrO, and othercomponents (if any) are chosen such that the glass includes, ascalculated in mole percent on an oxide basis: 64-68.2SiO₂, 11-13.5Al₂O₃,5-8B₂O₃, 2.5-6, MgO, 3-9CaO, and 1-3.5SrO.

In certain embodiments, the glasses of the present invention havedensities of less than about 2.6 g/cm³, such as densities of less than2.6 g/cm³, densities of less than about 2.56 g/cm³, densities of lessthan 2.56 g/cm³, densities of from about 2.4 g/cm³ to about 2.6 g/cm³,densities of from 2.4 g/cm³ to 2.6 g/cm³, densities of from about 2.45g/cm³ to about 2.6 g/cm³, densities of from 2.45 g/cm³ to 2.6 g/cm³,etc.

In certain embodiments, the glasses of the present invention haveliquidus temperatures of lower than or equal to about 1200° C., such asliquidus temperatures lower than or equal to about 1190° C., liquidustemperatures lower than or equal to about 1180° C., liquidustemperatures lower than or equal to about 1170° C., liquidustemperatures lower than or equal to about 1160° C., liquidustemperatures lower than or equal to about 1150° C., liquidustemperatures lower than or equal to about 1140° C., liquidustemperatures lower than or equal to about 1130° C., liquidustemperatures lower than or equal to about 1120° C., liquidustemperatures lower than or equal to about 1110° C., and liquidustemperatures lower than or equal to about 1100° C.

As mentioned above, the glasses of the present invention have liquidusviscosities of greater than or equal to about 90,000. Illustratively, incertain embodiments, the glasses of the present invention have liquidusviscosities of greater than or equal to 90,000 poises, such as greaterthan or equal to about 100,000 poises, greater than or equal to 100,000poises, greater than or equal to about 110,000 poises, greater than orequal to 110,000 poises, greater than or equal to about 120,000 poises,greater than or equal to 120,000 poises, greater than or equal to about130,000 poises, greater than or equal to 130,000 poises, greater than orequal to about 140,000 poises, greater than or equal to 140,000 poises,greater than or equal to about 150,000 poises, greater than or equal to150,000 poises, greater than or equal to about 160,000 poises, greaterthan or equal to 160,000 poises, greater than or equal to about 170,000poises, greater than or equal to 170,000 poises, greater than or equalto about 180,000 poises, greater than or equal to 180,000 poises, etc.

In certain embodiments, the glasses of the present invention have linearcoefficients of thermal expansion over the temperature range of 0° C. to300° C. of less than or equal to about 40×10⁻⁷/° C., such as less thanor equal to 40×10⁻⁷/° C.; less than or equal to about 39×10⁻⁷/° C.; lessthan or equal to 39×10⁻⁷/° C.; less than or equal to about 38×10⁻⁷/° C.;less than or equal to 38×10⁻⁷/° C.; less than or equal to about37×10⁻⁷/° C.; less than or equal to 37×10⁻⁷/° C.; less than or equal toabout 36×10⁻⁷/° C.; less than or equal to 36×10⁻⁷/° C.; from about33×10⁻⁷/° C. to about 40×10⁻⁷/° C.; from 33×10⁻⁷/° C. to 40×10⁻⁷/° C.:from about 33×10⁻⁷/° C. to about 36×10⁻⁷/° C.; from 33×10⁻⁷/° C. to36×10⁻⁷/° C.; etc.

In certain embodiments, the glasses of the present invention have strainpoints of greater than or equal to about 680° C., such as greater thanor equal to 680° C., greater than or equal to about 685° C., greaterthan or equal to 685° C., greater than or equal to about 690° C.,greater than or equal to 690° C., etc.

In certain embodiments, the glasses of the present invention have annealpoints of greater than or equal to about 725° C., such as greater thanor equal to 725° C., greater than or equal to about 730° C., greaterthan or equal to 730° C., greater than or equal to about 735° C.,greater than or equal to 735° C., greater than or equal to about 745°C., greater than or equal to 745° C., from about 725° C. to about 760°C., from 725° C. 760° C., from about 735° C. to about 760° C., from 735°C. to 760° C., etc.

In certain embodiments, the glasses of the present invention havemelting temperatures of less than or equal to about 1620° C., such asless than or equal to 1620° C., less than or equal to about 1615° C.,less than or equal to 1615° C., less than or equal to about 1610° C.,less than or equal to 1610° C., etc.

In certain embodiments, the glasses of the present invention havespecific moduli of greater than or equal to about 30.5 GPa·cc/g, such asgreater than or equal to 30.5 GPa·cc/g, greater than or equal to about31.5 GPa·cc/g, greater than or equal to 31.5 GPa·cc/g, etc.

The glasses can be produced in a variety of glass shapes, for example,glass plates (e.g., glass plates having a thickness of from about 30 μmto about 2 mm, such as from 30 μm to 2 mm, from about 100 μm to about 1mm, from 10 μm to 1 mm, etc.).

The sources of the various oxides contained in glasses of the presentinvention are not particularly critical. Batch ingredients can includefine sand, alumina, boric acid, magnesium oxide, limestone strontiumcarbonate, strontium nitrate, tin oxide, etc.

For example, SiO₂ is typically added as a crushed sand made of alphaquartz, either from loose sand deposits or mined from sandstone orquartzite. While these are commercially available at low cost, othercrystalline or amorphous forms of SiO₂ can be substituted in part or inwhole with little impact on melting behavior. Because molten SiO₂ isvery viscous and dissolves slowly into alkali-free glass, it isgenerally advantageous that the sand be crushed so that at least 85% ofit passes through a U.S. mesh size of 100, corresponding to mesh openingsizes of about 150 microns. In production, fines may be lofted by batchtransfer processes or by air-handling equipment, and, to avoid thehealth hazards this presents, it may be desirable to remove the smallestfraction of crushed sand as well.

Alumina is typically used as the source of Al₂O₃.

Boric acid is typically used as the source of B₂O₃.

In addition to the glass formers (SiO₂, Al₂O₃, and B₂O₃), the glasses ofthe invention also include MgO, CaO, and SrO. As known in the art, thealkaline earths are typically added as oxides (especially MgO),carbonates (CaO and SrO), nitrates (CaO and SrO), and/or hydroxides(MgO, CaO, and SrO). In the case of MgO and CaO, naturally-occurringminerals that can serve as sources include dolomite(Ca_(x),Mg_(1-x))CO₃), magnesite (MgCO₃), brucite (Mg(OH)₂), talc(Mg₃Si₄O₁₀(OH)₂), olivine (Mg₂SiO₄), and limestone (CaCO₃). Thesenatural sources include iron and so can be used as a way of adding thiscomponent in those cases where iron oxide is to be present in the glass.

The glasses of the invention can be manufactured using varioustechniques known in the art. For example, glass plates can be made usinga downdraw process, such as by a fusion downdraw process. Compared toother forming processes, such as the float process, the fusion processmay be preferred in certain circumstances for several reasons. Forexample, glass substrates made from the fusion process require lesspolishing or do not require polishing, depending, of course, on thedesired surface roughness of the final product. By way of furtherillustration, glass substrates made from the fusion process can havereduced average internal stress, relative to glasses made using otherprocesses.

The glasses of the present invention can be used in a variety ofapplications.

Illustratively, they can be used as a substrate for a siliconsemiconductor. For example, the glasses of the present invention can beused to make display glass substrates, such as display glass substrateshaving thicknesses of from about 30 μm to about 2 mm (e.g., from 30 μmto 2 mm, from about 100 μm to about 1 mm, from 10 μm to 1 mm, etc.).Examples of display glass substrates include TFT display glasssubstrates, such as a TFT display glass substrates for flat paneldisplay devices.

The present invention also relates to a semiconductor assembly thatincludes a semiconductor disposed on a glass substrate, wherein saidglass substrate comprises an alkali-free glass of the present invention.Examples of semiconductors that can be used in the aforementionedsemiconductor assemblies include transistors, diodes, silicontransistors, silicon diodes, and other silicon semiconductors; fieldeffect transistors (FETs), thin-film transistors (TFTs), organiclight-emitting diodes (OLEDs) and other light-emitting diodes; as wellas semiconductors that are useful in electro-optic (EO) applications, intwo photon mixing applications, in non-linear optical (NLO)applications, in electroluminescent applications, and in photovoltaicand sensor applications.

The present invention also relates to a flat panel display device thatincludes a flat, transparent glass substrate carrying polycrystallinesilicon thin film transistors, wherein said glass substrate comprises analkali-free glass of the present invention. The alkali-free glassincludes SiO₂, Al₂O₃, B₂O₃, MgO, CaO, and SrO such that, in mole percenton an oxide basis:64≦SiO₂≦68.2;11≦Al₂O₃≦13.5;5≦B₂O₃≦9;2≦MgO≦9;3≦CaO≦9; and1≦SrO≦5.Examples of suitable glasses from which the glass substrates can be madeinclude those discussed above, for example, glasses which satisfy thefollowing expressions: 1.05≦(MgO+CaO+SrO)/Al₂O₃≦1.45;0.67≦(SrO+CaO)/Al₂O₃≦0.92; and 0.45≦CaO/(CaO+SrO)≦0.95. Typically, inthe case of a flat panel display device, the device includes two plates(substrate assemblies) that are manufactured separately. One, the colorfilter plate, has a series of red, blue, green, and black organic dyesdeposited on it. Each of these primary colors corresponds precisely witha sub pixel of the companion active plate. The active plate, so calledbecause it contains the active, thin film transistors (TFTs), ismanufactured using typical semiconductor type processes. These includesputtering, CVD, photolithography, and etching.

In certain embodiments, the alkali-free glass used in the aforementionedsubstrates (e.g., display glass substrates) can be substantiallydefect-free. As discussed above, alkali-free glasses of the presentinvention that are substantially defect-free can be produced, forexample, by using one or more fining agents, such as SnO₂, Fe₂O₃, CeO₂,As₂O₃, Sb₂O₃, Cl, Br, or combinations thereof. Examples of suitablecombinations are set forth above. Illustratively, the glass can include,as fining agents, SnO₂ and Fe₂O₃; 0.02-0.3SnO₂ and 0.005-0.08Fe₂O₃; lessthan 0.05% by weight of Sb₂O₃ and/or As₂O₃; SnO₂, Fe₂O₃, CeO₂, Cl, Br,or combinations thereof but less than 0.05% by weight of Sb₂O₃ and/orAs₂O₃; SnO₂ and Fe₂O₃ but less than 0.05% by weight of Sb₂O₃ and/orAs₂O₃; and/or 0.02-0.3SnO₂ and 0.005-0.08Fe₂O₃ but less than 0.05% byweight of Sb₂O₃ and/or As₂O₃.

It is believed that the glasses of the present invention areparticularly advantageous in the manufacture of certain substrates foractive matrix liquid crystal display devices (AMLCDs). For example,AMLCD substrates optimally meet a variety of customer requirements,several of which are strongly dependent on the fusion process itself.One of these, a pristine surface, is believed to be an attribute offusion, and partially explains why customers are drawn to substratesmade by the fusion process. Another customer requirement is geometricstability under thermal cycling, and in this matter the fusion processsometimes comes up short. Because, in the fusion process, the glasstemperature decreases rather quickly from the forming temperatures(e.g., in excess of 1100° C.) to well below the glass transitiontemperature (e.g., about 720° C. for certain products), the glass has aslightly expanded volume relative to its fully relaxed state, or thestate that would be obtained if the glass were held near T_(g) for aconsiderable length of time. When the glass is reheated, it naturallyrelaxes towards its equilibrium volume, and this three-dimensionalcontraction or relaxation as sometimes referred to as “compaction”.

Illustratively, for a given draw (and its own specific cooling profile),and for a particular glass being made into a particular product (e.g.,thickness, area, etc.), the rate of cooling can be determined almostentirely by the rate (in inches per minute) at which the sheet comes offthe draw. This rate is sometimes referred to as the “pulling rollspeed”. From draw to draw, it has been found that increasing the pullingroll speed can increase compaction.

If melting takes place at a constant rate (e.g., 900 lbs per hour), thendelivering glass onto a longer isopipe slows down the rate at whichglass is removed, and hence lowers compaction. Thus, as larger sizes ofglass panel substrates are made on a particular tank, a reprieve (ofsorts) is obtained for the compaction problem. However, to improveefficiency, it is often desirable to make as many square feet of glassfrom a given draw as possible. One way to do this is to increase themelt rate, but this can push the system toward the compaction limit.This can be especially true of tanks with smaller isopipes, where highpulling roll rates can result in glasses close to acceptable limits ofcompaction (e.g., close to the compaction resulting from a 450° C.isothermal hold for one hour).

To pull more glass off of existing assets (i.e., without increasing thesize of tanks and isopipes), pulling roll rates can be increased, butthis may result in glasses having too high compaction. While it may bepossible to revamp the thermal profile of a draw so as to slow the rateof cooling through the critical viscosity region, thus reducingcompaction, there are practical limits to how far this can be taken. Forexample, at some point, the draw must become higher to allow for slowercooling at a high pulling roll speed, and this reinvigorates the problemof getting more glass out of an existing (as opposed to completelyredesigned and rebuilt) asset.

Research shows that isothermal holds of glasses produce less compactionas the strain or anneal point of a glass increases. FIG. 1 showscompaction after one hour at 450° C. for glasses with a range of annealpoints. Prior to the 450° C. heat treatment, the glasses were subjectedto a thermal cycle intended to be similar to the cooling profile of aglass coming off of a fusion draw (e.g., prolonged exposure to hightemperature, then rapid cooling at a rate similar to that used in afusion draw). As can be seen from FIG. 1, as anneal point increases,compaction decreases; however, above an anneal point of about 760° C.,the additional gain in compaction performance for a given increase inanneal point diminishes rapidly. The glasses with the highest annealpoint in FIG. 1 are intended for low-temperature polysilicon (“pSi”)applications.

By way of further illustration, the compositions of the presentinvention can be optimized so as to have liquidus viscosities of 90kpoise or greater, melting temperatures of 1620° C. or less, annealpoints of 725° C. or greater, and/or specific moduli of 30.5 GPa·cc/g orgreater. It is believed that compositions of the present inventionhaving a combination of high modulus and anneal point can especiallydesirable for use in certain fusion draw processes, such as for fusiondraw processes at high cooling rates.

While not intending to be bound or otherwise limited by any theory bywhich certain glasses of the present invention may operate, it isbelieved that elevated anneal points may provide enhanced geometricstability during amorphous silicon (“aSi”) processing and may permithigher draw speeds without recourse to annealing or expensive equipmentredesign. It is also believed (again, without intending to be limited byany theory by which certain glasses of the present invention mayoperate) that high level of fluxes and comparatively low meltingtemperatures can accelerate melting and, consequently, may allow forhigher melting rates without a corresponding increase in defects.

Compositions of the glasses of the invention can be determined usingquantitative analysis techniques well known in the art. Suitabletechniques are X-ray fluorescence spectrometry (XRF) for elements withan atomic number higher than 8, inductively coupled plasma opticalemission spectrometry (ICP-OES), inductively coupled plasma massspectrometry (ICP-MS), and electron microprobe analysis. See, forexample, J. Nolte, ICP Emission Spectrometry: A Practical Guide,Wiley-VCH (2003); H. E. Taylor, Inductively Coupled Plasma MassSpectroscopy: Practices and Techniques, Academic Press (2000); and S. J.B. Reed, Electron Microprobe Analysis, Cambridge University Press; 2ndedition (1997), which are hereby incorporated by reference. For ananalysis time of about 10 minutes for each element, detection limits ofapproximately 200 ppm for F and approximately 20 ppm for Cl, Br, Fe, andSn can be readily achieved using electron microprobe analysis. For traceelements, ICP-MS can be used.

The present invention is further illustrated by the followingnon-limiting examples.

EXAMPLES Example 1

This Example 1 and the following Examples 2 and 3 are meant to describehow the present invention was made. These Examples are not meant to, inany way, be limiting; instead, they are provided so that one skilled inthe art might have access to applicant's thought process and may usethis thought process, if appropriate, to further develop that which isdescribed here to optimize the glasses of the present invention for usein particular applications.

Several surprising insights led to this invention.

First was that the glasses with the best combination of liquidusviscosity, melting temperature, and anneal point tended to have similarproportions of SiO₂, Al₂O₃, MgO, CaO, and SrO when projected toB₂O₃-free compositions. To understand this, it is easiest to considerthe example of a single glass, which will also serve to introducevariables required for further discussion, the glass67SiO₂−9B₂O₃−11Al₂O₃−3MgO−7CaO−3SrO. This can be expressed as aB₂O₃-free glass as follows:[SiO₂]_(o)=SiO₂/(1−B₂O₃/100)=67/(1−9/100)=73.63[Al₂O₃]_(o)=Al₂O₃/(1−B₂O₃/100)=11/(1−9/100)=12.09[MgO]_(o)=MgO/(1−B₂O₃/100)=3/(1−9/100)=3.30[CaO]_(o)=CaO/(1−B₂O₃/100)=7/(1−9/100)=7.69[SrO]_(o)=SrO/(1−B₂O₃/100)=3/(1−9/100)=3.30The liquidus temperature of this glass is believed to be considerablyhigher than that of the glass that contains B₂O₃ because B₂O₃ dilutesthe concentrations of the other oxides and thus lowers their chemicalpotentials in the glass. It is further believed that, as B₂O₃ is addedto this composition, the liquidus temperature will decrease sharply,whereas viscosity will decrease more gradually. It is estimated that, atabout 5 mol % B₂O₃, the viscosity of the glass at the highesttemperature at which crystals form (the liquidus viscosity) will be >85kpoise, and the glass will be compatible with fusion, perhaps notexactly as generally practiced today, but well within reach of existingor planned adaptations to the process.

What may be most unexpected is that the B₂O₃-free analogs of glasseswithin the ranges of the glasses of the present invention tend to bevery similar to one another, and nearly always represent advantageouscombinations of high liquidus viscosity, low melting temperature, andhigh anneal point relative to glasses outside of these ranges. Forexample, a B₂O₃ glass containing no SrO at all would tend to have anunacceptably high liquidus temperature. B₂O₃ could be added andeventually a high liquidus viscosity might be obtained, but it wouldgenerally have too low an anneal point to facilitate high pull rates.This may be because CaO and MgO (particularly MgO) have unfavorableinteractions with SiO₂ and stabilize cristobalite (or anorthite)relative to a glass containing SrO in the range 2.5≦SrO≦5. To extendthis, consider a glass with no MgO but in which 1.05≦R_(o)≦1.45 (i.e.,1.05≦(MgO+CaO+SrO)/Al₂O₃≦1.45). In such a glass, S_(o) (i.e.,(SrO+CaO)/Al₂O₃) would be too high (i.e., outside of the range in which0.67≦S_(o)≦0.92. At fixed B₂O₃ concentration, the SiO₂ concentration ofsuch a glass could be manipulated so as to increase the liquidusviscosity, perhaps to a very high value, but the melting temperaturewould be far higher than that of a glass in which 0.67≦S_(o)≦0.92.Moreover, other attributes such as, CTE, density, and/or modulus (whichmay be of secondary importance, depending on the process by which theglass is to be formed and the use to which the glass is to be put) mayalso suffer relative to an analogous glass in which 0.67≦S_(o)≦0.92 and1.05≦R_(o)≦1.45. In other words, it is believed that many B₂O₃-freecompositions having S_(o) and/or R_(o) outside of, but close to, the0.67≦S_(o)≦0.92 and 1.05≦R_(o)≦1.45 ranges can be made compatible withfusion, but at a cost of anneal points that are perhaps too low and/ormelt temperatures that are perhaps too high.

The second surprising insight is that, as R_(o) increases, the glasswith the best combination of liquidus viscosity, melt temperature, andanneal point tends to have a higher MgO content than a glass with thesame B₂O₃ content but lower R_(o). Indeed, it is believed that there isa preferred MgO content determined by R_(o) and S_(o). This preferredMgO content is referred to as “[MgO]_(pred)”. Applicant has determined[MgO]_(pred) empirically to be approximated by:[MgO]_(pred)=[1.29+12.94×R_(o)−14.4×S_(o)]×[1−B₂O₃/100]For a given R_(o) and S_(o), it is believed that, when the differencebetween MgO and [MgO]_(pred) is small, the glass will have at least twoof the following: an advantageous liquidus viscosity, an advantageousmelting temperature, an advantageous anneal point. It is furtherbelieved that glasses having all three advantageous properties (i.e., anadvantageous liquidus viscosity, an advantageous melting temperature,and an advantageous anneal point) can be obtained when−0.3≦MgO−[MgO]_(pred)≦0.3.

The third surprising insight is that glasses with the best combinationsof liquidus viscosity, melting temperature, and anneal point and5≦B₂O₃≦9 tend to have SiO₂ contents that are determined largely by theMgO content, R_(o) value, and S_(o) value of the glass. As is the casewith MgO, it is believed that there is a preferred SiO₂ contentdetermined by MgO, R_(o), and S_(o) (this preferred SiO₂ content beingreferred to as “[SiO₂]_(pred)”), but, for fixed R_(o) and S_(o), MgOwill be determined in part by the level of B₂O₃ in the glass. Therefore,it is believed that the preferred value of SiO₂ must be calculated usingthe MgO concentration of the B₂O₃-free analog of the composition inquestion, e.g., from above.[MgO]_(o)=MgO/(1−B₂O₃/100).With this, applicant has determined [SiO₂]_(pred) to be approximated by:[SiO₂]_(pred)=[87.57−6.06×MgO/B_(o)+66.54×R_(o)−80.61×S_(o)]×B_(o)in which B_(o)=1−B₂O₃/100. It is believed that, when the differencebetween SiO₂ and [SiO₂]_(pred) is small, the glass will have at leasttwo of the following: an advantageous liquidus viscosity, anadvantageous melting temperature, an advantageous anneal point. It isfurther believed that glasses having all three advantageous properties(i.e., an advantageous liquidus viscosity, an advantageous meltingtemperature, and an advantageous anneal point) can be obtained when−0.3≦SiO₂−[SiO₂]_(pred)≦0.3.

To see the interplay between these variables, and to see how to use therelationships set forth in this Example 1 to optimize the glasses of thepresent invention for particular applications, Examples 2 and 3 areprovided below.

Example 2

This Example 2 illustrates a procedure for testing a glass compositionto determine whether it is particularly well suited for use in fusionprocesses, the use of [MgO]_(pred) and [SiO₂]_(pred) to optimize theglasses of the present invention for use in fusion processes.

Consider the glass discussed in Example 1,67SiO₂−9B₂O₃−11Al₂O₃−3MgO−7CaO−3SrO. As a preliminary matter, simpleinspection reveals that the glass's oxide components lie within thefollowing ranges:64≦SiO₂≦68.2;11≦Al₂O₃≦13.5;5≦B₂O₃≦9;2≦MgO≦9;3≦CaO≦9; and1≦SrO≦5.Moreover, a simple calculation shows that the expressions(MgO+CaO+SrO)/Al₂O₃=(3+7+3)/11=1.18; (SrO+CaO)/Al₂O₃=(3+7)/11=0.91; andCaO/(CaO+SrO)=7/(7+3)=0.7 lie within the following ranges:1.05≦(MgO+CaO+SrO)/Al₂O₃≦1.45;0.67≦(SrO+CaO)/Al₂O₃≦0.92; and0.45≦CaO/(CaO+SrO)≦0.95.

Using the expressions given above, R_(o), S_(o), C_(o), and [MgO]_(o)can be calculated as follows:R_(o)=(MgO+CaO+SrO)/Al₂O₃=(3+7+3)/11=1.18S_(o)=(CaO+SrO)/Al₂O₃=(7+3)/11=0.91C_(o)=CaO/(CaO+SrO)=7/(7+3)=0.7[MgO]_(o)=MgO/(1−B₂O₃/100)=3/(1−9/100)=3.30The values for R_(o), S_(o), C_(o), and [MgO]_(o) can then be used tocalculate the values of [MgO]_(pred) and [SiO₂]_(pred), as follows:[MgO]_(pred)=[1.29+12.94×R_(o)−14.4×S_(o)]×[1−B₂O₃/100]=[1.29+(12.94)(1.18)−(14.4)(0.91)]×[1−9/100]=3.18[SiO]_(pred)=[87.57−6.06×MgO/B_(o)+66.54×R_(o)−80.61×S_(o)]×B_(o)=[87.57−(6.06)(3.3)+(66.54)(1.18)−(80.61)(0.91)]×[1−9/100]=66.94Using these [MgO]_(pred) and [SiO₂]_(pred) values, the expressionsMgO−[MgO]_(pred) and for SiO₂−[SiO₂]_(pred) can be determined asfollows:MgO−[MgO]_(pred)=3−3.18=−0.18,SiO₂−[SiO₂]_(pred)=67−66.94=0.06

Thus, the glass composition used in this example (i.e.,SiO₂−9B₂O₃−11Al₂O₃−3MgO−7CaO−3SrO) satisfies the expressions:−0.3≦MgO−[MgO]_(pred)≦0.3−0.3≦SiO₂−[SiO₂]_(pred)≦0.3.It is believed that, for example, relative to glasses with the sameR_(o) and S_(o) values but with MgO or SiO₂ concentrations outside ofthe preferred ranges (i.e., those concentrations of MgO which differfrom [MgO]_(pred) by more than 0.3 and those concentrations of SiO₂which differ from [SiO₂]_(pred) by more than 0.3 and, especially,relative to glasses with MgO or SiO₂ concentrations that lie outside ofthe ranges 64≦SiO₂≦68.2 and 2≦MgO≦9, the glass in the example(67SiO₂−9B₂O₃−11Al₂O₃−3MgO−7CaO−3SrO) will tend to have a bettercombination of liquidus viscosity, melting temperature, and anneal pointfor use in certain processes (such as in fusion processes).

The process described above in this Example 2 can be repeated for avariety of candidate glass compositions to determine the glasscompositions' [MgO]_(pred) and [SiO₂]_(pred) values. It is believedthat, by comparing the [MgO]_(pred) and [SiO₂]_(pred) values with theMgO and SiO₂ concentrations in the candidate glasses, one can obtainglasses that may have particularly desirable combinations of liquidusviscosity, melting temperature, and anneal point for use in certainprocesses, such as in fusion processes.

Example 3

This Example 3 illustrates a procedure for generating a glasscomposition using the relationships described in Example 1.

The procedure involves the following steps:

-   -   (1) selecting an anneal point target;    -   (2) selecting trial values for R_(o) and S_(o);    -   (3) calculating [MgO]_(o) using R_(o) and S_(o);    -   (4) calculating [SiO₂]_(o) using [MgO]_(o) as the target value        for MgO;    -   (5) calculating [Al₂O₃]_(o), [CaO]_(o), and [SrO]_(o) using        R_(o), S_(o), [MgO]_(o) and [SiO₂]_(o);    -   (6) calculating B₂O₃ and using it to calculate the renormalized        concentrations of SiO₂, B₂O₃, Al₂O₃, MgO and CaO; and    -   (7) comparing the result with desired density and CTE targets,        and if necessary perform steps 1-6 again with new input        parameters.

To perform these steps, we take advantage of three empiricalrelationships describing the composition dependence of anneal point,coefficient of thermal expansion, and density, viz.:Anneal point=828.3+3.1Al₂O₃−3.9MgO−4.0CaO−4.4SrO−9.4B₂O₃(° C.)CTE=13.6+0.22B₂O₃+0.75MgO+1.58CaO+1.86SrO (×10⁻⁷/° C.)Density=2.189+0.0088Al₂O₃−0.0046B₂O₃+0.0100MgO+0.0131CaO+0.0286SrO(g/cm³)

The first step is to select an anneal point target. Anneal points of740° C. or more afford a substantial increase in pull rate, but annealpoints above 760° C. may offer little improvement with regard to aSiapplications. If the glass were intended for a larger size sheet,however, it is possible that a lower anneal point might suffice, asmelting rate might be the limiting factor. In this example, anintermediate target value of 748° C. was selected.

The next step is to select starting values for R_(o), S_(o) and C_(o).The relationship between these variables and the properties of the finalglass are complex, as one may be adjusted against the other to obtain arange of properties. With this in mind, and putting aside for thepresent the question of liquidus viscosity (and hence compatibility withfusion), it is believed that, generally:

-   -   high values of R_(o) result in low melting temperatures, low        anneal points, high CTEs and high densities relative to lower        R_(o) values;    -   high values of S_(o) result in high melting temperatures, high        CTEs, relatively low anneal points, and high densities relative        to lower S_(o) values;    -   High values of C_(o) result in lower melting temperatures,        higher CTEs, high anneal points, and high densities.        Given the trends for C_(o), it might seem attractive to make it        as high as possible (1.0), but in fact this tends to drive up        liquidus temperatures, and thus diminish liquidus viscosities.

Since the CTEs and densities of glasses of the present invention arealmost invariably well-suited for AMLCD applications, it is more usuallythe case to try to obtain some balance between the competing attributesof liquidus viscosity, melting temperature, and anneal point, thenadjust a reference composition so as to improve density or CTE. For thisexample, the following R_(o), S_(o), and C_(o) values are selected so asto be close to the mid-points of their respective ranges: R_(o)=1.23,S_(o)=0.82, and C_(o)=0.65.

With these R_(o), S_(o), and C_(o) values in hand, steps (3) and (4) areperformed. More particularly, a target MgO content for a referenceB₂O₃-free glass is calculated as follows:[MgO]_(o)=1.29+12.94×R_(o)−14.4×S_(o)=5.4 mol %.Using [MgO]_(o) as input, the idealized SiO₂ content of the referenceB₂O₃-free glass is calculated as follows:[SiO₂]_(o)=87.57−6.06×[MgO]_(o)+66.54×R_(o)−80.61×S_(o)=70.59 mol %.

With these values, step (5) can be performed to determine Al₂O₃, CaO,and SrO contents for the reference B₂O₃-free glass:[Al₂O₃]_(o)+[CaO]_(o)+[SrO]_(o)=100−[SiO₂]_(o)−[MgO]_(o)=24 mol %Since[CaO+SrO]_(o)/[Al₂O₃]_(o)=0.82,combining the previous two expressions yields:1.82[Al₂O₃]_(o)=24 mol %and, solving for [Al₂O₃]_(o), one obtains[Al₂O₃]_(o)=13.19 mol %.The combined concentration of CaO and SrO are determined by difference:[CaO+SrO]_(o)=24−13.19=10.81 mol %.Since by assumption [CaO]_(o)/[CaO+SrO]_(o)=0.65,the values of [CaO]_(o) and [SrO]_(o) are obtained as follows:[CaO]_(o)=(0.65)×(10.81)=7.03 mol %[SrO]_(o)=3.78 mol %

Using these oxide concentrations (which are pertinent to a B₂O₃-freeglass), step (6) can be performed. In step (6), the anneal pointalgorithm presented above is used to determine how much B₂O₃ must beadded to produce the desired anneal point. Substituting the expressionsof the form [M_(x)O_(y)]_(o)=M_(x)O_(y)×(1−B₂O₃/100) into the annealpoint expression, where M_(x)O_(y) represents Al₂O₃, MgO, CaO, and SrO,the following expression is obtained:Annealpoint=828.3+3.1[Al₂O₃]_(o)×(1−B₂O₃/100)−3.9[MgO]_(o)×(1−B₂O₃/100)−4.0[CaO]_(o)×(1−B₂O₃/100)−4.4[SrO]_(o)×(1−B₂O₃/100)−9.4B₂O₃DefiningK_(o)=3.1[Al₂O₃]_(o)−3.9[MgO]_(o)−4[CaO]_(o)−4.4[SrO]_(o)the following expression is obtained:Anneal point=828.3+K_(o)−B₂O₃×K_(o)/100−9.4[B₂O₃]_(o).With further rearrangement, this expression yieldsB₂O₃=(828.3−anneal point+K_(o))/(K_(o)/100+9.4).For the composition under consideration,K_(o)=(3.1)×(13.19)−(3.9)×(5.4)−(4)×(7.03)−(4.4)×(3.78)=−24.9Substituting this and the target anneal point of 748° C. into theexpression for B₂O₃, the value for B₂O₃ is calculated:B₂O₃=(828.3−748−24.923)/(−24.9/100+9.4)=6.05 mol %.The calculated value for B₂O₃ can now be used to renormalize theconcentrations of the other oxides. For example,SiO₂=[SiO₂]_(o)×(1−6.05/100)=66.32 mol %.The final composition isSiO₂=66.32Al₂O₃=12.39B₂O₃=6.05MgO=5.07CaO=6.60SrO=3.55

Finally, in Step (7), values for CTE and density are calculated toconfirm that they are appropriate for the application in mind:CTE=13.6+0.22B₂O₃+0.75MgO+1.58CaO+1.86SrOCTE=35.8×10⁻⁷/° C.andDensity=2.189+0.0088Al₂O₃−0.0046B₂O₃+0.0100MgO+0.0131CaO+0.0286SrODensity=2.509 g/cm³.

Both values fall well within the ranges of commercially-available LCDcompositions. If lower CTE or density is required, then lower values forR_(o) and/or a higher S_(o) may drive the properties in the correctsense, albeit perhaps at the expense of other attributes, such asmelting temperature or liquidus viscosity. The best balance depends uponthe processes envisioned for manufacturing the glass and limitations onattributes dictated by customer requirements.

It is believed that glasses in which the SiO₂, Al₂O₃, B₂O₃, MgO, CaO,SrO, and other components (if any) are chosen such that the glassincludes, as calculated in mole percent on an oxide basis: 64-68.2SiO₂,11-13.5Al₂O₃, 5-9B₂O₃, 2-9, MgO, 3-9CaO, and 1-5SrO have one or more(e.g., two or more, three or more, etc.) of the following advantageousproperties: melting temperature less than or equal to 1620° C. (e.g.,less than or equal to 1615° C., less than or equal to 1610° C., etc.);anneal point greater than or equal to 725° C. (e.g., greater than orequal to 730° C., greater than or equal to 735° C., greater than orequal to 740° C., greater than or equal to 745° C., etc.); liquidusviscosities of greater than or equal to 90 kilopoises (e.g., greaterthan or equal to 100 kilopoises, greater than or equal to 110kilopoises, greater than or equal to 130 kilopoises. etc.). The datapresented in Table 1 below confirm this.

When one migrates outside of the aforementioned ranges (i.e., outside of64-68.2SiO₂, 11-13.5Al₂O₃, 5-9B₂O₃, 2-9, MgO, 3-9CaO, and 1-5SrO), onemight be able to find glasses having one or more of the above-citedadvantageous properties, but, in view of the analysis presented in thisExample 3, operating outside these ranges will likely impact one or moreof the above-cited properties in a particularly unfavorable way. Forexample, it is believed that having a higher SiO₂ content may adverselyaffect the melting point: having a higher B₂O₃ content may adverselyaffect anneal point; having a lower B₂O₃ content and/or a lower SiO₂content may adversely affect liquidus viscosity; etc.

Moreover, as noted above, in certain embodiments, the glass componentsare selected such that the expression 1.05≦(MgO+CaO+SrO)/Al₂O₃≦1.45 issatisfied. These glasses are believed to possess particularly goodanneal points and liquidus viscosities, compared to anneal points when(MgO+CaO+SrO)/Al₂O₃>1.45 and liquidus viscosities when(MgO+CaO+SrO)/Al₂O₃<1.05.

Examples 4-103

Table 1 lists examples of glasses of the present invention in terms ofmole percents which are either calculated on an oxide basis from theglass batches. Table 1 also lists various physical properties for theseglasses, the units for these properties being as follows:

Strain Point ° C. Anneal Point ° C. Softening Point ° C. CTE ×10⁻⁷/° C.(0-300° C.) Density grams/centimeter³ Melting Temp. ° C. Liquidus Temp.° C. Liquidus Viscosity kilopoise

Inasmuch as the sum of the individual constituents totals or veryclosely approximates 100, for all practical purposes, the reportedvalues may be deemed to represent mole percent. The actual batchingredients may comprise any materials, either oxides, or othercompounds, which, when melted together with the other batch components,will be converted into the desired oxide in the proper proportions. Forexample, SrCO₃ and CaCO₃ can provide the source of SrO and CaO,respectively.

The specific batch ingredients used to prepare the glasses of Table 1were fine sand, alumina, boric acid, magnesium oxide, limestone, andstrontium carbonate or strontium nitrate.

The glasses set forth in Table 1 were prepared by melting 3,000 or19,000 gram batches of each glass composition at a temperature and timeto result in a relatively homogeneous glass composition, e.g., at atemperature of about 1600° C. for a period of about 16 hours in platinumcrucibles. In particular, the batch materials were ball-milled for onehour using ceramic media in a ceramic mill. The batch was transferred toan 1800 cc platinum crucible and loaded into a furnace at 1600° C. After16 hours, the crucible was removed from the furnace and the glass waspoured onto a cold steel plate. When viscous enough to handle, the glasswas transferred to an annealing oven at 725° C., held for one hour atthis temperature, then cooled at 0.5° C./minute to room temperature.

The glass properties set forth in Table 1 were determined in accordancewith techniques conventional in the glass art. For example, the linearcoefficient of thermal expansion (CTE) over the temperature range 0-300°C. is expressed in terms of ×10⁻⁷/° C. and the strain point is expressedin terms of ° C. These were determined from fiber elongation techniques(ASTM references E228-85 and C336, respectively). The density in termsof grams/cm³ was measured via the Archimedes method (ASTM C693). Themelting temperature in terms of ° C. (defined as the temperature atwhich the glass melt demonstrates a viscosity of 200 poises (“T @ 200p”)) was calculated employing a Fulcher equation fit to high temperatureviscosity data measured via rotating cylinders viscometry (ASTMC965-81). The liquidus temperature of the glass in terms of ° C. wasmeasured using the standard gradient boat liquidus method of ASTMC829-81. This involves placing crushed glass particles in a platinumboat, placing the boat in a furnace having a region of gradienttemperatures, heating the boat in an appropriate temperature region for24 hours, and determining by means of microscopic examination thehighest temperature at which crystals appear in the interior of theglass. The liquidus viscosity in kilopoises was determined from theliquidus temperature and the coefficients of the Fulcher equation.

TABLE 1 Example 4 5 6 7 8 9 10 11 SiO₂ 64.44 66.55 66.31 67.84 66.1567.32 67.24 67.5 Al₂O₃ 11.95 12.5 12.48 12.58 12.5 12.27 12.18 12.63B₂O₃ 6.51 6.45 5.49 6 6.6 5.99 7.09 6.34 MgO 6.47 4.65 5.21 3.29 5 4.234.31 3.69 CaO 7.4 6.6 6.16 6.69 6.1 6.52 7.85 5.29 SrO 3.23 3.25 4.233.6 3.65 3.51 1.22 4.55 R_(o) 1.43 1.16 1.25 1.08 1.18 1.16 1.10 1.07S_(o) 0.89 0.79 0.83 0.82 0.78 0.82 0.74 0.78 C_(o) 0.70 0.67 0.59 0.650.63 0.65 0.87 0.54 [SiO₂]_(pred) 64.55 66.45 66.30 67.89 66.01 67.3967.30 67.55 SiO₂ − [SiO₂]_(pred) −0.11 0.09 0.01 −0.05 0.13 −0.07 −0.06−0.04 [MgO]_(pred) 6.53 4.63 5.17 3.26 4.97 4.27 4.44 3.67 MgO₂ −[MgO]_(pred) −0.06 0.02 0.04 0.03 0.03 −0.04 −0.13 0.02 strain point 685689 706 700 687 701 698 701 anneal point 735 741 751 755 738 754 749 754softening point 959 972 981 991 970 986 982 988 CTE 37.5 35 36.5 36.935.2 34.5 33.2 35 density 2.520 2.498 2.525 2.495 2.506 2.499 2.4482.509 melting point 1535 1579 1586 1604 1572 1604 1593 1609 liquidustemperature 1120 1165 1170 1175 1155 1165 1180 1170 liquidus viscosity149 102 109 124 110 152 90 135 Example 12 13 14 15 16 17 18 19 SiO₂67.41 65.24 68.39 68.09 67.78 67 65.68 65.24 Al₂O₃ 12.65 12.36 12.8312.14 12.19 12.57 12.32 12.28 B₂O₃ 5.84 7.58 3.99 6.35 6.2 5.42 7.686.99 MgO 4.07 4.77 4.47 3.11 3.58 4.73 4.97 5.12 CaO 6.26 6.31 6.44 6.676.6 6.42 5.97 6.07 SrO 3.6 3.74 3.71 3.51 3.52 3.69 3.38 4.18 R_(o) 1.101.20 1.14 1.09 1.12 1.18 1.16 1.25 S_(o) 0.78 0.81 0.79 0.84 0.83 0.800.76 0.83 C_(o) 0.63 0.63 0.63 0.66 0.65 0.64 0.64 0.59 [SiO₂]_(pred)67.56 65.12 68.49 68.06 67.79 67.07 65.56 65.23 SiO₂ − [SiO₂]_(pred)−0.14 0.11 −0.1 0.03 −0.01 −0.07 0.11 0.01 [MgO]_(pred) 4.05 4.70 4.453.15 3.62 4.71 4.98 5.07 MgO₂ − [MgO]_(pred) 0.02 0.07 0.02 −0.04 −0.040.02 −0.01 0.05 strain point 702 685 725 697 698 704 680 685 annealpoint 756 737 777 751 753 758 732 737 softening point 995 971 1009 994991 988 966 965 CTE 34.1 35.2 35.4 33.8 34.8 35.7 34.9 39.9 density2.501 2.496 2.521 2.487 2.492 2.512 2.481 2.514 melting point 1605 15561617 1618 1613 1596 1573 1567 liquidus temperature 1160 1140 1195 11601165 1160 1150 1150 liquidus viscosity 199 126 115 194 167 174 111 121Example 20 21 22 23 24 25 26 27 SiO₂ 66.84 64.13 63.94 65.17 66.38 67.666.42 64.7 Al₂O₃ 12.38 12.36 12.23 12.83 12.53 12.2 12.46 12.18 B₂O₃5.74 7.77 8.19 7.79 5.5 7.05 6.72 7.8 MgO 5.01 5.03 5.66 4.69 5.15 3.554.34 5.06 CaO 6.4 6.98 6.83 5.58 7.51 5.85 6.28 6.01 SrO 3.5 3.73 3.153.83 2.81 3.75 3.6 4.13 R_(o) 1.20 1.27 1.28 1.10 1.23 1.08 1.14 1.25S_(o) 0.80 0.87 0.82 0.73 0.82 0.79 0.79 0.83 C_(o) 0.65 0.65 0.68 0.590.73 0.61 0.64 0.59 [SiO₂]_(pred) 66.88 63.96 63.74 65.15 66.37 67.5466.53 64.69 SiO₂ − [SiO₂]_(pred) −0.04 0.16 0.18 0.02 0.01 0.06 −0.110.01 [MgO]_(pred) 5.04 4.87 5.58 4.56 5.10 3.62 4.32 5.02 MgO₂ −[MgO]_(pred) −0.03 0.16 0.08 0.13 0.05 −0.07 0.02 0.04 strain point 699678 677 698 704 686 694 682 anneal point 752 730 728 742 756 741 747 734softening point 982 958 957 970 984 981 979 964 CTE 35.1 36.9 36 34.636.2 33.7 34.5 36.1 density 2.508 2.509 2.492 2.495 2.505 2.485 2.4912.506 melting point 1589 1535 1540 1573 1587 1607 1588 1566 liquidustemperature 1180 1100 1130 1155 1175 1150 1140 1120 liquidus viscosity91 254 105 125 96 198 228 234 Example 28 29 30 31 32 33 34 35 SiO₂ 67.6666.85 66.1 67.64 66.89 66.33 66.01 66.83 Al₂O₃ 12.7 12.28 12.2 12.4612.67 12.48 12.32 12.76 B₂O₃ 5 5.41 6.2 6.33 5.48 5.49 5.49 5.5 MgO 4.425.12 5.7 3.88 5.52 5.79 5.35 4.93 CaO 6.38 6.06 6.05 5.13 5.51 6.3 6.958.12 SrO 3.67 4.17 3.75 4.56 3.79 3.49 3.74 1.74 R_(o) 1.14 1.25 1.271.09 1.17 1.25 1.30 1.16 S_(o) 0.79 0.83 0.80 0.78 0.73 0.78 0.87 0.77C_(o) 0.63 0.59 0.62 0.53 0.59 0.64 0.65 0.82 [SiO₂]_(pred) 67.76 66.8966.06 67.61 66.84 66.32 66.05 66.81 SiO₂ − [SiO₂]_(pred) −0.1 −0.04 0.040.02 0.04 0.01 −0.04 0.02 [MgO]_(pred) 4.40 5.16 5.78 3.91 5.54 5.815.32 4.87 MgO₂ − [MgO]_(pred) 0.02 −0.04 −0.08 −0.03 −0.02 −0.02 0.030.06 strain point 714 712 687 697 705 710 693 705 anneal point 766 756739 750 757 754 746 758 softening point 1001 983 966 982 985 983 973 988CTE 35.2 36.2 34.9 34.6 34 35.9 37.2 34.7 density 2.514 2.522 2.5152.508 2.513 2.513 2.525 2.471 melting point 1602 1594 1580 n.d. 15971582 1579 1593 liquidus temperature 1180 1175 1160 1160 1175 1165 11501180 liquidus viscosity 118 99 102 n.d. 108 114 144 92 Example 36 37 3839 40 41 42 43 SiO₂ 66.58 66.79 66.8 67.01 66.56 66.8 67.24 64.84 Al₂O₃12.48 12.25 12.5 12.58 12.37 12.5 12.18 12.38 B₂O₃ 6.5 5.49 5.4 5.5 5.485.4 7.09 7.79 MgO 4.36 5.12 5.73 4.61 5.15 4.59 3.32 4.96 CaO 6.29 7.224.97 7.21 7.29 6.12 8.84 4.94 SrO 3.61 2.99 4.59 2.96 3.01 4.59 1.224.95 R_(o) 1.14 1.25 1.22 1.17 1.25 1.22 1.10 1.20 S_(o) 0.79 0.83 0.760.81 0.83 0.86 0.83 0.80 C_(o) 0.64 0.71 0.52 0.71 0.71 0.57 0.88 0.50[SiO₂]_(pred) 66.69 66.87 66.68 67.05 66.60 66.69 67.27 64.83 SiO₂ −[SiO₂]_(pred) −0.1 −0.07 0.11 −0.03 −0.04 0.1 −0.03 0.01 [MgO]_(pred)4.34 5.17 5.77 4.57 5.15 4.52 3.34 4.89 MgO₂ − [MgO]_(pred) 0.02 −0.05−0.04 0.04 0 0.07 −0.02 0.07 strain point 702 700 702 705 700 694 697679 anneal point 754 753 755 757 753 746 751 731 softening point 984 982994 987 983 977 987 964 CTE 34.9 35.5 34.4 35.4 36 37.1 33.9 35.8density 2.502 2.505 2.526 2.503 2.510 2.538 2.448 2.518 melting point1593 1592 n.d. 1601 1589 n.d. 1595 1558 liquidus temperature 1155 11751185 1185 1165 1160 1180 1160 liquidus viscosity 174 101 n.d. 89 123n.d. 94 87 Example 44 45 46 47 48 49 50 51 SiO₂ 67.66 68.03 67.21 66.367.32 67.5 65.04 67.73 Al₂O₃ 12.08 12.77 12.61 12.47 12.27 12.18 12.4812.56 B₂O₃ 7.13 4.5 5.64 5.49 5.99 7.03 6.89 5.99 MgO 3.42 4.44 4.39 5.74.23 3.54 5.13 3.29 CaO 6.47 6.4 6.34 7.02 6.52 5.84 6.89 6.67 SrO 3.243.69 3.64 2.89 3.51 3.74 3.57 3.59 R_(o) 1.09 1.14 1.14 1.25 1.16 1.081.25 1.08 S_(o) 0.80 0.79 0.79 0.79 0.82 0.79 0.84 0.82 C_(o) 0.67 0.630.64 0.71 0.65 0.61 0.66 0.65 [SiO₂]_(pred) 67.55 68.13 67.31 66.3067.39 67.60 64.87 67.94 SiO₂ − [SiO₂]_(pred) 0.1 −0.1 −0.1 0 −0.07 −0.10.16 −0.2 [MgO]_(pred) 3.50 4.42 4.37 5.71 4.27 3.62 5.00 3.26 MgO₂ −[MgO]_(pred) −0.08 0.02 0.02 −0.01 −0.04 −0.08 0.13 0.03 strain point686 720 706 701 701 700 689 696 anneal point 741 771 759 753 754 753 741749 softening point 983 1006 988 979 986 986 964 987 CTE 36 34.7 34.732.4 34.5 34.6 36.5 34.2 density 2.474 2.517 2.506 2.504 2.499 2.5012.511 2.487 melting point 1602 1613 1599 1585 1600 1608 1556 n.d.liquidus temperature 1150 1185 1170 1170 1165 1170 1120 1150 liquidusviscosity 185 122 151 99 149 131 191 n.d. Example 52 53 54 55 56 57 5859 SiO₂ 67.56 66.84 67.95 66.7 66.59 66.06 66.24 66.6 Al₂O₃ 12.06 12.3311.95 12.5 12.63 12.52 12.41 12.57 B₂O₃ 7.12 6.98 6.7 6.15 5.5 6 6.515.5 MgO 3.41 3.99 3.4 4.7 5.04 5.17 4.67 5.56 CaO 6.46 5.69 6.15 6.057.77 6.66 6.35 6.83 SrO 3.24 3.99 3.85 3.9 2.34 3.59 3.64 2.81 R_(o)1.09 1.11 1.12 1.17 1.20 1.23 1.18 1.21 S_(o) 0.80 0.79 0.84 0.80 0.800.82 0.80 0.77 C_(o) 0.67 0.59 0.62 0.61 0.77 0.65 0.64 0.71[SiO₂]_(pred) 67.59 66.97 67.75 66.60 66.58 65.91 66.32 66.57 SiO₂ −[SiO₂]_(pred) −0.03 −0.12 0.19 0.09 0.01 0.14 −0.08 0.03 [MgO]_(pred)3.49 4.02 3.48 4.68 4.99 5.10 4.65 5.57 MgO₂ − [MgO]_(pred) −0.08 −0.03−0.08 0.02 0.05 0.07 0.02 −0.01 strain point 696 696 687 689 703 692 694703 anneal point 750 749 741 742 755 745 746 755 softening point 989 986981 978 986 977 981 983 CTE 34 33.8 35.7 34.6 36.2 35.9 35.1 34.8density 2.479 2.488 2.489 2.506 2.495 2.514 2.503 2.501 melting point1607 1601 1600 1589 1587 1570 1587 1590 liquidus temperature 1160 11501150 1150 1175 1140 1145 1170 liquidus viscosity 188 216 188 156 93 172177 100 Example 60 61 62 63 64 65 66 67 SiO₂ 66.48 66.99 66.01 67.6865.22 67.45 66.62 66.85 Al₂O₃ 12.81 11.71 13.07 11.86 11.42 12.05 12.4212.31 B₂O₃ 6 6.92 6 7.62 8.41 6.65 5.5 5.5 MgO 4.23 5.06 4.23 3.44 4.53.75 5.1 5.06 CaO 6.81 4.51 6.95 6.3 6.33 6.2 7.44 7.38 SrO 3.67 4.813.74 3.1 4 3.9 2.78 2.76 R_(o) 1.15 1.23 1.14 1.08 1.30 1.15 1.23 1.23S_(o) 0.82 0.80 0.82 0.79 0.90 0.84 0.82 0.82 C_(o) 0.65 0.48 0.65 0.670.61 0.61 0.73 0.73 [SiO₂]_(pred) 66.47 67.10 66.06 67.53 65.26 67.3166.65 66.91 SiO₂ − [SiO₂]_(pred) 0.01 −0.1 −0.05 0.14 −0.04 0.13 −0.03−0.06 [MgO]_(pred) 4.09 5.32 4.01 3.58 4.63 3.81 5.10 5.10 MgO₂ −[MgO]_(pred) 0.14 −0.26 0.22 −0.14 −0.13 −0.06 0 −0.04 strain point 698682 699 683 676 687 704 704 anneal point 751 735 752 736 725 740 755 755softening point 987 974 985 984 957 980 985 986 CTE 36.1 35.9 38.1 33.536.3 34.8 35.7 36.1 density 2.511 2.505 2.514 2.471 2.494 2.496 2.5022.501 melting point 1583 1586 1578 n.d. 1557 1598 1592 1596 liquidustemperature 1165 1150 1170 1150 1120 1145 1180 1180 liquidus viscosity116 136 103 n.d. 172 189 88 92 Example 68 69 70 71 72 73 74 75 SiO₂64.98 65.94 67.55 66.83 67.57 67.4 65.15 67.54 Al₂O₃ 12.59 12.42 12.7312.99 12 12.25 12.34 11.78 B₂O₃ 7.8 5.99 6.05 5.55 7.62 6.75 7.56 8.2MgO 4.83 5.18 3.74 4.24 3.28 3.5 4.77 3.02 CaO 4.84 6.12 6.2 7.44 6.435.75 6.29 7.01 SrO 4.83 4.22 3.56 2.95 3.1 4.35 3.73 2.45 R_(o) 1.151.25 1.06 1.13 1.07 1.11 1.20 1.06 S_(o) 0.77 0.83 0.77 0.80 0.79 0.820.81 0.80 C_(o) 0.50 0.59 0.64 0.72 0.67 0.57 0.63 0.74 [SiO₂]_(pred)64.96 65.94 67.78 66.84 67.46 67.33 65.19 67.34 SiO₂ − [SiO₂]_(pred)0.02 0 −0.22 −0.01 0.1 0.07 −0.04 0.18 [MgO]_(pred) 4.73 5.13 3.72 4.093.38 3.51 4.71 3.14 MgO₂ − [MgO]_(pred) 0.1 0.05 0.02 0.15 −0.1 −0.010.06 −0.12 strain point 685 702 701 706 687 687 688 679 anneal point 735747 754 759 742 740 739 733 softening point 964 975 990 993 987 979 971967 CTE 39.9 36 34.4 35.1 33.2 35 35.1 33.3 density 2.541 2.523 2.4972.503 2.462 2.502 2.497 2.448 melting point 1564 1595 1595 1589 n.d.1609 1583 n.d. liquidus temperature 1125 1170 1140 1165 1145 1150 11501135 liquidus viscosity 219 116 269 137 n.d. 184 142 n.d. Example 76 7778 79 80 81 82 83 SiO₂ 67.16 66.94 65.59 66.58 64.68 65.37 66.32 64.23Al₂O₃ 12.8 12.56 12.34 12.58 12.18 12.03 12.48 11.91 B₂O₃ 5.87 5.99 6.495.48 7.79 5.49 5.49 8.38 MgO 3.8 4.39 5.15 5.68 6.02 6.09 5.81 5.2 CaO6.56 6.31 6.1 5.65 4.61 7.09 5.79 7.03 SrO 3.81 3.63 4.2 3.89 4.61 3.824 3.25 R_(o) 1.11 1.14 1.25 1.21 1.25 1.41 1.25 1.30 S_(o) 0.81 0.790.83 0.76 0.76 0.91 0.78 0.86 C_(o) 0.63 0.63 0.59 0.59 0.50 0.65 0.590.68 [SiO₂]_(pred) 67.22 67.05 65.59 66.55 64.65 65.56 66.29 64.15 SiO₂− [SiO₂]_(pred) −0.06 −0.1 0 0.03 0.03 −0.18 0.02 0.08 [MgO]_(pred) 3.704.37 5.11 5.69 6.07 6.15 5.83 5.19 MgO₂ − [MgO]_(pred) 0.1 0.02 0.04−0.01 −0.05 −0.06 −0.02 0.01 strain point 705 704 688 706 683 690 708677 anneal point 759 756 740 757 731 741 753 727 softening point 992 987969 987 960 966 981 954 CTE 35.9 35.1 37.7 35.7 35.9 37.3 35.7 35.8density 2.506 2.505 2.518 2.513 2.513 2.532 2.521 2.492 melting point1599 1588 1576 1599 1557 1566 1588 1549 liquidus temperature 1160 11651155 1170 1120 1150 1170 1130 liquidus viscosity 170 129 117 114 203 116110 100 Example 84 85 86 87 88 89 90 91 SiO₂ 66.77 67.24 67.76 64.4 64.767.15 67.42 67.09 Al₂O₃ 12.58 12.18 11.52 11.6 12.18 12.5 12.29 12.26B₂O₃ 7.12 7.09 8.19 7.8 7.8 7.05 6 5.84 MgO 3.71 4.31 3.33 5.4 5.06 3.354.23 4.21 CaO 6.13 7.85 6.75 6.4 6.01 5.7 6.54 7.03 SrO 3.52 1.22 2.454.4 4.13 4.25 3.52 3.57 R_(o) 1.06 1.10 1.09 1.40 1.25 1.06 1.16 1.21S_(o) 0.77 0.74 0.80 0.93 0.83 0.80 0.82 0.86 C_(o) 0.64 0.87 0.73 0.590.59 0.57 0.65 0.66 [SiO₂]_(pred) 67.00 67.30 67.52 64.45 64.69 67.2267.33 66.97 SiO₂ − [SiO₂]_(pred) −0.21 −0.06 0.22 −0.05 0.01 −0.07 0.080.11 [MgO]_(pred) 3.69 4.44 3.54 5.47 5.02 3.33 4.26 4.19 MgO₂ −[MgO]_(pred) 0.02 −0.13 −0.21 −0.07 0.04 0.02 −0.03 0.02 strain point697 694 703 677 685 689 697 698 anneal point 751 748 757 727 732 742 751751 softening point 985 983 994 950 959 982 992 985 CTE 34.4 33 34.238.4 36 34.6 36.2 36.3 density 2.493 2.445 2.492 2.518 2.509 2.496 2.4962.509 melting point 1597 1601 1607 1549 1566 1597 1602 1587 liquidustemperature 1160 1175 1150 1100 1120 1150 1175 1170 liquidus viscosity171 96 193 264 226 190 119 99 Example 92 93 94 95 96 97 98 99 SiO₂ 64.3266.95 66.31 66.89 66 66.87 66.62 66.8 Al₂O₃ 11.59 12.35 12.47 12.6711.92 12.5 12.51 12.6 B₂O₃ 7.8 7 5.5 5.49 6.26 5.5 6.92 6.7 MgO 5.4 4 75.41 5.01 4.34 4.02 4.15 CaO 6.38 5.7 5.59 6.66 6.92 6.93 6.2 6.45 SrO4.39 4 3.01 2.74 3.89 3.74 3.56 3.3 R_(o) 1.40 1.11 1.25 1.17 1.33 1.201.10 1.10 S_(o) 0.93 0.79 0.69 0.74 0.91 0.85 0.78 0.77 C_(o) 0.59 0.590.65 0.71 0.64 0.65 0.64 0.66 [SiO₂]_(pred) 64.50 66.91 66.29 66.8665.94 66.89 66.77 66.78 SiO₂ − [SiO₂]_(pred) −0.16 0.04 0.02 0.03 0.06−0.02 −0.14 0.02 [MgO]_(pred) 5.48 4.02 7.14 5.42 5.05 4.27 4.00 4.12MgO₂ − [MgO]_(pred) −0.08 −0.02 −0.14 −0.01 −0.04 0.07 0.02 0.03 strainpoint 675 685 711 706 689 699 694 689 anneal point 725 738 756 758 741752 748 742 softening point 951 980 978 988 969 984 979 977 CTE 37.135.2 34.6 34.3 37.6 36.4 34.2 34.7 density 2.516 2.495 2.505 2.498 2.5192.513 2.491 2.491 melting point 1551 1592 1581 1591 1565 1595 1592 1594liquidus temperature 1120 1150 1170 1170 1160 1165 1145 1140 liquidusviscosity 159 159 104 116 87 132 217 223 Example 100 101 102 103 SiO₂67.3 65.72 66.59 65.14 Al₂O₃ 12.63 12.44 12.38 12.83 B₂O₃ 5.5 6.74 5.457.79 MgO 4.41 5.02 5.16 4.71 CaO 6.35 6.4 6.11 4.7 SrO 3.65 3.68 4.24.71 R_(o) 1.14 1.21 1.25 1.10 S_(o) 0.79 0.81 0.83 0.73 C_(o) 0.64 0.630.59 0.50 [SiO₂]_(pred) 67.39 65.58 66.60 65.12 SiO₂ − [SiO₂]_(pred)−0.09 0.13 −0.01 0.02 [MgO]_(pred) 4.39 4.96 5.16 4.58 MgO₂ −[MgO]_(pred) 0.02 0.06 0 0.13 strain point 710 685 707 694 anneal point762 737 753 740 softening point 992 968 983 970 CTE 34.9 35.8 35.3 35.2density 2.507 2.503 2.520 2.512 melting point 1599 1565 1600 1573liquidus temperature 1170 1160 1180 1150

From Table 1, it can be seen that the compositions that satisfy theexpressions:−0.3≦MgO−[MgO]_(pred)≦0.3−0.3≦SiO₂−[SiO₂]_(pred)≦0.3have liquidus viscosities of at least 90 kpoise, and are therefore arecompatible with fusion as practiced today, or can be made compatiblewith fusion with minimal adjustment to current processes. Forcomparison, the nominal liquidus viscosity of Corning's Eagle XG is 130kpoise, and devitrification within the quality area has never been seenfor this glass in production. This is because of its comparatively steepviscosity curve, which permits a smaller ΔT across the isopipe. Sincesome glasses set forth in Table 1 have melting temperatures comparableto or lower than Eagle XG and anneal points higher than Eagle XG, theyhave still steeper viscosity curves, and so a slightly lower liquidusviscosity is believed to be acceptable. Of course, many of the glasseshave liquidus viscosities comparable to or greater than Eagle XG, and,for these, the risk is much smaller.

FIG. 2 is a plot of SiO₂ concentration for various glasses of thepresent invention vs.[87.46−5.85×MgO×(1−B₂O₃/100)+63.67×M_(a)−13.85×S_(o)]×[1−B₂O₃/100], thepredictive measure for SiO₂. FIG. 3 is a plot of MgO for various glassesof the present invention vs.[1.01+12.77×R_(o)−13.79×S_(o)]×[1−B₂O₃/100], the predictive measure forMgO. As FIGS. 2 and 3 show, the actual concentrations of MgO and SiO₂lie very close to the predicted values for all compositions.

FIG. 4 is a graph of melting temperature of various glasses of thepresent invention as a function of SiO₂ content. As FIG. 4 shows, themelting temperature increases as a relatively steep function of SiO₂content for glasses that otherwise satisfy the expressions:11≦Al₂O₃≦13.5; 5≦B₂O₃≦9; 2≦MgO≦9; 3≦CaO≦9; and 1≦SrO≦5. Accordingly, itis believed that, when SiO₂ content is above 68.2 mol %, meltingtemperatures higher than 1620° C. may result, particularly incompositions that do not contain arsenic.

Although preferred embodiments have been depicted and described indetail herein, it will be apparent to those skilled in the relevant artthat various modifications, additions, substitutions and the like can bemade without departing from the spirit of the invention and these aretherefore considered to be within the scope of the invention, as definedin the claims which follow.

The invention claimed is:
 1. An alkali-free glass having a liquidusviscosity of greater than or equal to about 90,000 poises, a meltingtemperature less than or equal to about 1620° C.. and an anneal pointgreater than or equal to about 725° C., said glass comprising SiO₂,Al₂O₃, B₂O₃, MgO, CaO, SrO, SnO₂, and Fe₂O₃, such that, in mole percenton an oxide basis: 64≦SiO₂≦68.2; 11≦Al₂O₃≦13.5; 5≦B₂O₃≦9; 2≦MgO≦9;3≦CaO≦9; 1≦SrO≦5; 0.02≦SnO₂≦0.3; and 0.005≦Fe₂O₃≦0.08; wherein: (i) theglass comprises less than 0.05% by weight of Sb₂O₃, As₂O₃, orcombinations thereof; (ii) the BaO content of the glass on an oxidebasis is less than 1000 ppm by weight; and (iii) the glass is in theform of a plate produced by a fusion draw process.
 2. An alkali-freeglass according to claim 1 wherein said glass has a liquidus viscosityof greater than or equal to about 100,000 poises and a liquidustemperature of lower than or equal to about 1200° C.
 3. An alkali-freeglass according to claim 1 wherein said glass has a linear coefficientof thermal expansion over the temperature range of 0° C. to 300° C. ofless than or equal to about 40×10⁻⁷/° C.
 4. An alkali-free glassaccording to claim 1, wherein, in mole percent on an oxide basis:11.3≦Al₂O₃≦13.5.
 5. An alkali-free glass according to claim 1, wherein,in mole percent on an oxide basis:1.05≦(MgO+CaO+SrO)/Al₂O₃≦1.45;0.67≦(SrO+CaO)/Al₂O₃≦0.92; and0.45≦CaO/(CaO+SrO)≦0.9; and the glass has a liquidus temperature oflower than or equal to about 1200° C.
 6. An alkali-free glass accordingto claim 1, wherein, in mole percent on an oxide basis:1.05≦(MgO+CaO+SrO)/Al₂O₃≦1.3;0.72≦(SrO+CaO)/Al₂O₃≦0.9; and0.55≦CaO/(CaO+SrO)≦0.9.
 7. An alkali-free glass according to claim 1,wherein, in mole percent on an oxide basis:1.05≦(MgO+CaO+SrO)/Al₂O₃≦1.3;0.72≦(SrO+CaO)/Al₂O₃≦0.9; and0.8≦CaO/(CaO+SrO)≦0.9.
 8. An alkali-free glass according to claim 1wherein the glass contains one or more of CeO₂, and Br.
 9. Analkali-free glass according to claim 1, wherein in mole percent:F+Cl+Br≦0.4.
 10. An alkali-free glass according to claim 1, wherein saidglass has a liquidus viscosity of greater than or equal to about 100,000poises.
 11. An alkali-free glass according to claim 1, wherein saidglass has a liquidus viscosity of greater than or equal to about 130,000poises.
 12. An alkali-free glass according to claim 1, wherein saidglass has a liquidus temperature of lower than or equal to about 1200°C.
 13. A glass substrate, such as a display glass substrate, comprisingan alkali-free glass according to claim
 1. 14. A glass substrateaccording to claim 13, wherein the alkali-free glass is substantiallydefect-free glass substrate is a display glass substrate.
 15. A flatpanel display device comprising a flat, transparent glass substratecarrying polycrystalline silicon thin film transistors, wherein saidglass substrate comprises an alkali-free glass according to claim
 1. 16.A method of making a glass plate comprising melting, fining, and formingbatch materials so that the glass of the glass plate is alkali-free andcomprises SiO₂, Al₂O₃, B₂O₃, MgO, CaO, and SrO, wherein the methodcomprises using the following relationships to select the batchmaterials:1.05≦R_(o)≦1.45;0.67≦S_(o)≦0.92; and0.45≦C_(o)≦0.95; where R_(o), S_(o), and C_(o) are given by:R_(o)=(MgO+CaO+SrO)/Al₂O₃;S_(o)=(CaO+SrO)/Al₂O₃; andC_(o)=CaO/(CaO+SrO); where Al₂O₃, MgO, CaO, and SrO are in mole percenton an oxide basis.
 17. The method of claim 16 wherein the glass plate isformed by a downdraw process.
 18. The method of claim 17 wherein thedowndraw process is a fusion downdraw process.
 19. The method of claim16 further comprising using the glass plate as a substrate for a siliconsemiconductor.
 20. The method of claim 16 further comprising using theglass plate as a substrate for a flat panel display device.
 21. A methodof making a glass plate comprising melting, fining, and forming batchmaterials so that the glass of the glass plate is alkali-free andcomprises SiO₂, Al₂O₃, B₂O₃, MgO, CaO, and SrO; where, in mole percenton an oxide basis:64≦SiO₂≦68.2;11≦Al₂O₃≦13.5;5≦B₂O₃≦9;2≦MgO≦9;3≦CaO≦9; and1≦SrO≦4.5; and where: (i) the glass of the glass plate has a liquidusviscosity greater than or equal to about 90,000 poises; (ii) the glassof the glass plate has an anneal point greater than or equal to about725° C.; and (iii) the BaO content of the glass of the glass plate on anoxide basis is less than 1000 ppm by weight.
 22. The method of claim 21wherein the glass plate is formed by a downdraw process.
 23. The methodof claim 22 wherein the downdraw process is a fusion downdraw process.24. The method of claim 21 further comprising using the glass plate as asubstrate for a silicon semiconductor.
 25. The method of claim 21further comprising using the glass plate as a substrate for a flat paneldisplay device.